The subject invention relates to a parking brake system for a vehicle having an electronic braking system where the parking brake system includes a dual hand control that includes electronic and pneumatic elements to actuate a latching cylinder to mechanically lock a service brake in a parked condition.
Traditionally, heavy commercial vehicles utilize spring actuators to provide the energy needed for parking. Typically, a hand operated lever or handle is moved by an operator into a park position, which causes the spring actuators to be applied. A valve that works on an inverse air principle controls the spring actuators. The valve releases air pressure in response to a parking command, to allow the spring force of the spring actuators at each wheel to apply the brake. During vehicle operation, i.e. under normal driving conditions when parking is not required, the air pressure in the system is sufficient to overcome the spring force in the spring actuators allowing free rotation of the wheel.
One disadvantage with this conventional parking system is that the spring actuators are bulky, heavy, and expensive. This system is especially disadvantageous on front steering axles where packaging space is at a premium. In certain axle configurations, it is not possible to install the spring actuators because there is simply not enough room.
Thus, there is a need for a parking brake system that eliminates the spring actuators while still providing a pneumatically controlled and mechanically lockable park brake that can operate in an electronically controlled parking brake system.